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Avalanche Institute

 

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Crust

Also: Rain Crust, Sun Crust, Wind Crust, Melt-Freeze Crust

A crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind.

A Rain Crust is formed by the freezing of infiltrated rain water. It can be thin (from a glaze to a few millimeters thick) or if there is hard rain there may be more of an ice surface than a distinct crust.

A Sun Crust is formed by the freezing of sun melted surface snow. It is usually thin, between a glaze and a few millimeters thick.

A Wind Crust is formed when the winds deposit a hard packed later of blown snow, or scour the surface hard. These are often found on windward slopes.

A Melt-Freeze Crust results from a period of melt-freeze metamorphism and is typically a few centimeters thick.

Because they contain more ice than other layers in the snowpack buried crusts can alter the temperature gradient locally, and kinetic growth grain forms (such as facets or sugar snow) sometimes form more readily adjacent to a crust.

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